Examples of known molding systems are (amongst others): (i) the HyPET (trademark) Molding System, (ii) the Quadloc (Trademark) Molding System, (iii) the Hylectric (trademark) Molding System, and (iv) the HyMET (trademark) Molding System, all manufactured by Husky Injection Molding Systems (Location: Canada; www.husky.ca).
FIG. 1A depicts a known hot-runner nozzle system associated with U.S. Pat. No. 4,450,999 (Inventor: GELLERT; Published: May 29, 1984) which discloses: (i) a hot tip nozzle seal for use in a sprue gated injection molding system, and (ii) a method of manufacture. The nozzle seal has a cylindrical outer portion, an elongated central pin portion and a number of ribs extending therebetween to define a number of apertures through the nozzle seal. The outer portion is seated in both the heated nozzle and the cavity plate to bridge the insulative air gap between them. The central pin portion of the seal has a tip portion which extends downstream into the gate and a head portion which extends upstream into the nozzle bore. The central pin portion has an inner conductive portion formed of copper and an outer protective casing formed of steel. The seal is designed so that the head portion picks up a predetermined amount of heat from the surrounding melt and transfers it through the highly conductive copper to the tip portion which extends to where it is required, without being unacceptably susceptible to abrasion or corrosion from difficult materials such as glass filled flame retardant nylon. The seal is made by integrally filling the steel pin casing with copper in a vacuum furnace. The filled casing is then brazed into a body portion with the ribs and a cap brazed on in the vacuum furnace to provide the integral abrasion and corrosion resistant nozzle seal.
FIG. 1B depicts a known hot-runner nozzle system associated with U.S. Pat. No. 5,098,280 (Inventor: TRAKAS; Published: Mar. 24, 1992), which discloses a gating needle for use in an injection molding sprue bushing that has an elongated central needle portion and at least three radially extending members which extend radially outwardly from the central needle portion. The gating needle is seated in an annular cavity or circular recess disposed at the outlet end of a sprue bushing and is capable of slight axial movement due to the action of the injected melt flowing around it so that the needle maintains a constant position and clearance within the mold cavity gate. The gating needle may include an interior heat transfer portion in the form of either a highly thermally conductive metal core portion or in the form of a sealed hollow tube containing a vaporizable liquid. The interior heat transfer portion transfers heat from the surrounding melt to the mold cavity gate to maintain the mold cavity gate area at a constant temperature.
FIG. 1C depicts a known hot-runner nozzle system associated with U.S. Pat. No. 5,206,040 (Inventor: GELLERT; Published: Apr. 27, 1993), which discloses a hot tip gated injection molding apparatus having a heated manifold to distribute melt to a number of spaced gates. An unheated sealing and conductive member is mounted directly between the heated manifold and the cooled cavity plate in alignment with each gate. The sealing and conductive member has an elongated hot tip shaft which is connected to extend centrally through the bore of an outer collar portion by a number of spaced spiral blades. The collar portion bridges an insulative air space between the hot manifold and cooled cavity plate to prevent melt leaking into it. Heat received through the rear end of the collar portion which abuts directly against the heated manifold is transferred through the blades and the hot tip shaft to the gate area which is aligned with the pointed forward end of the hot tip shaft. The rear end of the hot tip shaft extends rearwardly into a branch of the melt passage to pick up heat from the surrounding melt. The hot tip shaft has a highly conductive inner portion inside an abrasion resistant outer portion to conduct heat to and away from the gate area during different parts of the injection cycle. The spiral blades impart a swirling motion to the melt which flows between them.
FIG. 1D depicts a known hot-runner nozzle system associated with U.S. Pat. No. 5,284,436 (Inventor: GELLERT; Published: Feb. 8, 1994), which discloses an injection molding apparatus wherein a torpedo is mounted in the front end of a heated nozzle. The torpedo has spaced blades extending inwardly from an outer collar to an elongated shaft which extends centrally in the melt bore. The torpedo shaft has an elongated central portion which is securely press fitted in a steel outer sleeve from which the blades extend. The elongated central portion of the torpedo shaft extends forwardly into the gate, and is formed of an engineered ceramic such as silicon carbide which is very thermally conductive as well as abrasion and corrosion resistant. In one embodiment, the gate extends through a gate insert which is also formed of a thermally conductive and abrasion and corrosion resistant engineered ceramic material.
FIG. 1E depicts a known hot-runner nozzle system associated with U.S. Pat. No. 5,318,434 (Inventor: GELLERT; Published: Jun. 7, 1994), which discloses an injection molding apparatus wherein a torpedo is mounted at the front end of a nozzle to provide a fixed ring gate. The torpedo has an elongated central shaft with a nose portion which projects forwardly into a cylindrical opening extending through the mold to the cavity. The outer surface of the nose portion is sufficiently spaced from the inner surface of the opening to form the ring gate through which the melt flows into the cavity. The nose portion of the central shaft enhances heat transfer during the injection cycle and thus reduces cycle time and provides cleaner gates.
FIG. 1F depicts a known hot-runner nozzle system associated with U.S. Pat. No. 5,405,258 (Inventor: BABIN; Published: Apr. 11, 1995), which discloses an injection molding apparatus for hot tip gating wherein a torpedo is screwed into a threaded seat in the forward end of a nozzle. The torpedo has an elongated shaft with a pointed tip mounted centrally in an outer collar by a pair of spiral blades which impart a swirling motion to the melt flowing to the gate. The temperature of the melt in the gate varies according to a continuous thermodynamic cycle in the torpedo. A thermocouple bore extends radially inward through the outer collar and one of the spiral blades to a conductive inner portion of the central shaft of the torpedo. The thermocouple bore is positioned whereby a thermocouple element extends radially outward from it into an insulative air space between the forward end of the nozzle and the mold. The thermocouple element has a substantially 90 degree rearward bend a predetermined distance from its inner end. The bend abuts against a tapered portion of the inner surface of the well in which the nozzle is seated to securely retain the thermocouple element against the inner end of the thermocouple bore. This accurate location and reliable retention of the thermocouple element in place provides the accurate monitoring of the melt temperature necessary for its control throughout the thermodynamic cycle.
FIG. 2A depicts a known screw-in nozzle tip. Based on high-pressure testing and high-temperature testing, the inventor found that the known screw-in nozzle tip systems may prematurely unscrew due to loss of preload at very high temperatures. The inventor's analysis also indicates that the nozzle tip may be inadequate for such extreme operating conditions.
FIG. 2B depicts a known nozzle tip, which are made with copper alloys that are held to the nozzle housing by their flange and using a steel retainer. The inventor's testing and analysis indicates that high pressures and temperatures may crack a tip flange during operation. The high-stress concentration resulting from an abrupt change in cross-section (that is, from the outer diameter of the nozzle tip to the outer diameter of the flange) may be undesirable for such operating conditions; as well, variation in thermal expansion amongst connected materials also inadvertently and disadvantageously raises stresses.
FIG. 2C depicts a known hot-runner nozzle system, in which a copper alloy tip lasts longer than other known nozzle systems at high pressures. The flange of the tip is tapered in this case to reduce the stress concentration. However, the inventor found that these tips also fail when the temperature was raised to 350° C.